Heating



April 26, 1938. N; c. ARTSAY HEATING 2 Sheets-Sheet 1 Filed April 27,1955 INVENTOR.

NICHOLAS CARTJAY ATTO EY.

April 1938. N. c.-ARTsAY 2,115,548

HEATING I Filed April 27, 1935 2 Sheets-Sheet 2 INVENTOR. /V/CHOL/45 6'.427124) ATTORN Patented Apr. 26, 1938 r HEATING Nicholas 0. Artsay,Valhalla, N. Y., a... to Foster Wheeler Corporation, New York, N. Y., a

corporation of New York I Application April 2'1, 1935, Serial No. 10,572

4 Claims. (01; 122-43) This invention relates to heating processes andapparatus.

In many industrial plants, especially chemical plants, there is a needfor heating processes in the range of 500 to 700 F. in which thetemperature oi. heating elements must be constant and uniformthroughout. This result,

in the lower range of temperature, is usually attained by condensingsteam. However, the higher temperature range involves steam pressuresfrom 650 to 3000 lbs. per 'sq. in. which necessitates special boilerinstallations and large expense. To reduce the operating vapor pressuresnecessary, other fluids or materials such as the l5 diphenyloxldes, havebeen employed. In most cases, the high temperature range processes areof intermittent character and considerable inconvenience is experiencedin. starting up the special boiler after each shut down. Instead ofemploying special boilers for this purpose, it has .been found moredesirable to draw the needed amounts of heat from steam or other vaporproduced by a boiler already on the line. There are several knownmethods of incorporating high pressure steaming elements in ordinary lowpressure boilers and 'these arrangements throttle down the high pressuresteam to the pressureinthe mains when the higher pressures are notneeded.

' This involves the installation of a high pressure feed pump and thecontamination of the high pressure heating surfaces with the boiler feedwater which may be satisfactory for the low pressure boiler'but isundesirable for the high pres-' sure elements. The high pressure feedpump can 5 be eliminated, if desired, to make the circuit aclosedcircuit and return the condensate by gravity, however, thethrottling of unneeded steam is.

then impossible so'that another place of condensation must be provided.If this place of con- 40 densation is a coil in the boiler drum, thehigh pressure heating elements should be placed considerably above theboiler drum to provide for the gravity return of condensate. Thisinvolves great difliculties in a great "majority-of boiler designs 45gfifi'cannot be done at all with boilers already steam and also to anyother heat carrying fluid used in the system. A condensate pump can beinstalled which is located in a sumclently low 50 position to draw theliquid and return it to the heating elements, but if water is used as afluid, the pump must be constructed to stand the high pressure andnecessarily will be expensive. Moreover, the circulating means mustalways be op- "sting o to insure the reliahil tv of bo ler oner- Thisconsideration applies both to water ation and to comply with the boilerstatutes, at least two circulating pumps will be required.

The present invention provides a novel heating method and apparatuswhich overcomes all these difficulties. In general, the arrangement 5includes a fluid heater placed outside an ordinary heater, such as asteam boiler, the fluid to be heated and vaporized being circulated by apump through the tubes in one or more circuits.- The fluid or othermaterial to be heated may be 10 any substance having a sufllciently highboiling point for the purpose desired. Such materials will includediphcnyloxides, 'or a mixture of diphenyl and diphenyloxide, mercury,high boiling point oils, and concentrated solutions of certain salts. 15Part of the hot gases passing through the boiler or other heater isdiverted into the fluid heater and after being cooled by giving up heatto the fluid, it is returned into a'lower temperature zone of the boileror its eccnomizer or air heater. When the fluid is only partly vaporizedin the heater, the arrangement preferably includes a separator whichreturns the liquid phase to the pump, and the vapor is conducted to theplace of heat consumption. A distributing valve is em- 25 played todivert part of the vapor into cooling processes after which the steam iscontaminated and the condensate made worthless for further use. The safeoperation of a high pressure steaming element subject to hot gasesrequires the use of distilled water for feeding, which is.

often unavailable. I For these cases, thearrangement embodying theinvention may include a drum in which high pressure steam is generatedby means of heating elements in which the heating vapor is condensed.This arrangement eliminates thedanger of overheating or burning the highpressure tubes.

The heating process and apparatus of the invention and its novelfeatures'will be understood from the'following description whenconsidered in connection with the accompanying drawings, in

which:

Fig. 1 is a more or less diagrammatic view in vertical section, ofapparatus embodying the inventlon; and

Fig. 2 is a similar view showing another form of the invention.

Like reference characters refer to the same or similar parts in bothviews.

The invention will be described and illustrated in connection with steamboilers and with part of the products of combustion produced in thefurnaces of the boilers being utilized to heat the fluid by means ofwhich heat is supplied to the process or other desired points or zones.Itwill be understood however that the invention amt limited in itsapplication to steam boilers but that it also may be utilized inconnection with heaters in general or other sources of heat.

Referring to the form of invention shown in Fig. 1, reference characterl0 designates a straight tube stoker fired boiler of conventionaldesign. Any other boiler design may be employed, if desired. The boilershown has a furnace li, a steam and water drum l2, banks of boiler tubesl3 and an economizer i4 in a flue IS. A superheater I6 is located in thefirst of the three passes l1, l8 and [9. During operation of the boiler,part of the combustion gases are withdrawn from the furnace at 20 andare led through a refractory lined duct 2i into a two-pass fluid heater22. It is understood that the gases may also be withdrawn from any otherconvenient high temperature zone of the boiler. The heater 22 has aheating coil 23 extending through both passes, and the tubes in thecooler second pass are fltted with extended surfaces 24. Obviously, theheater may have a single pass or more than two passes and the tubes ofthe heating coil may all be bare or may all be fltted with extendedsurfaces. After being-drawn through the heater, the gases enter 'anoutlet duct 25 and are delivered by a fan 26 into an outlet duct 21which discharges into the flue l5 below the economlzer. A circulatingpump 21' takes the 'fluid to be heated in the liquid phase from a surgetank 23 and delivers it through pipe 23 having a check valve 33, andpipe 3| to heating coil 23. After being vaporized to the extent desiredincoil 23, the fluid enters a vapor separator 32. The liquid Phasethrown down in the separator 32, returns through a trap 33 and pipe 34to the surge tank 23, while the separated vapor flows through pipe 36into a distributing valve 36 having a piston 31 which controls theinlets to pipes 33 and 33, so that when the inlet to one of these pipesis closed the other is open. Valve 36 is controlled in response to thepressure of-the fluid in pipe 33 and is normally urged in a position toclose the inlet to pipe 33 by a spring 43. lfrom the valve 34 the vapormay be led through pipe 33 to the condensing coil 4! placed in theboiler drum and/or to the process heating coils 42 shown as a bank oftubes heating a fluid in a tank 43 through pipe 33 and control valve 44.The process heating is controlled by the valve 44 and a check valve 46in the fluids condensate returnpipe 44 which connects through pipe 41,loop seal 43 and pipe 34 with the surge tank. The fluids condensate inthe boiler drum coil v surge tank through pipe 43 which connects withpipe 41. The heater 22 produces an amount of fluid's vapor in proportionto the amount and temperature of the gases drawn through it? The boilermay be running at variable load and hence the amount of gases for agiven amount of heat extraction will be variable also. The amount ofheat extraction as manifested by the vapor pressure may be regulatedinany known manner. In thisinstaneathevaporpressureimpulseis trans- 4'iis returned also to the.

ferred by the pipe 50 to a pressure responsive device 5l which controlsthe pneumatically actuated cylinder 52 which in turn operates andcontrols the damper 53 in duct 21. If desired, the pressure responsivedevice 5| or the like may be arranged to control the speed of the fan26. For any given amount of heat extraction, the vapor pressure in thefluid circuit will depend on the proportion of vapor flowing into thecoil 42 and the coilv 4!, the latter being surrounded by boiler water ata substantially lower temperature than that of the process fluid in thetank 43. For proper heating effect in the tank 43, the pressure of vaporin the pipe 39 before the process valve 45, is maintained constant bythe distributing valve 36. Whenever vapor pressure in the pipe 39decreases, the valve 36 reduces the flow into the coil 4| and increasesthe flow to the coil 42 and vice versa. Thus during the operation thevapor pressure in the coils 4i and 42 will be tending to be difierent,but substantially lower in the former. To make the control ofdistribution more effective, a slight over-pressure will be maintainedbefore the distributing valve 36 by proper setting of the device. Whenthe process valve 44 is open, the vapor pressure in the fluid condensatelines 46, 49, and 41 and the surge tank 23 will be equal to the pressurein the process coil 42 which means that the return of condensate fromthecoil 4i through the pipe 49 will be impeded and consequently the coil 4|will be flooded with condensate up to a certain level when the remainingvapor condensing surface of high heat transfer rate will be sufllcientlysmall to give an undercooling to the condensate in the coil 4 i, and areduced flow of vapor to maintain the vapor pressure and effect thereturn of condensate. When the process valve 44 is closed at the end ofthe process operation, the vapor pressure in pipe 33 will rise and thevalve 36 will close the inlet to the pipe 33 and open more the inlet tothe pipe 33 leading to the coil 4|. This will result in the purging ofthe coil 4i and the restoration of the full heat transfer capacity bymeans of which all of the heat extracted from the boiler gases some ofthe gases will nevertheless pass the heater 22 and the vapor generatedat such times will be condensed in the coil 4|. Shouldit be desired toshut down the circulating pump 21', a by-pass 6! controlled by a valve56 and which connects ,pipe 41 at loop seal 43 with pipe 3i provides acircuit of natural circulation for the fluid. Qheck valve 33 willprevent flow into the surge tank through the pump 21' when the pump isnot operating.

Since most of the high boiling point substances which are suitable aresolids at moderate room temperatures, when the boiler is shut down, thefluid is drained to the surge tank 28 from the heater, by opening thevalve 51 in line 53 which connects pipes 23 and 34. In the surge tank,the substances can remain solid without inconvenience and can be meltedwhen needed either by the higher boiler room temperature or by using asmall steam coil around the tank 23.

In the form of the invention shown in Fig. 2, a boiler of the Stirlingtype is employed. This boiler is designated generally 30 and has afur-'nace 8i, drums 32, 43,34 and 46, which are. connected by boiler tubes 63in the usual manner. 76

" The combustion gases after flowing over the boiler tubes, aredelivered to an air heater i1 through a duct 68 and thence out to a fluepr stack. High pressure steam, for instance at 1500 lbs. per sq. in., isgenerated in the drum I placed in a vertical position preferably. Thedrum is fitted with blow down valves "II at the bottom to purge it frommud and concentrated solids in the feed water which enters through thevalve I2 in pipe 13. The steam generated in the drum is taken outthrough pipe 14 controlled by a stop valve I5. Heat is. supplied forvaporizing the- I water in the drum 10 by condensing the vapor ofdiphenyloxideor other suitable substance in a heating coil 16 disposedin the drum and connected with the vapor and condensate pipes. Due tothe relatively low temperature inside the tubes of the coil Hi, there isno danger'in scale accumulation on their outer surface and consequentlyordinary feed water can be'supplied for high pressure steam generation.The degree of scale accumulation will be observable through the vaporpressure of the substance employed (or temperature diiference) for agiven high pressure steam output. The method of descaling these tubeswill be hereinafter described.

The'pump 21' circulates diphenyloxide or other substance through theheater 22 which is supplied, by va controlled amount of furnace gasdrawn through the heater by the fan 26, ashereinbefore described. Thevapor and liquid mixture is passed through the separator 32 and theseparated liquid is returned to the surge tank 28, while the vapor isled to the distributing valve 38.

.In this case, the distributing valve is responsive to and is regulatedto maintain the desired pressure of steam in the 'drum Ill. Wheneversteam. pressure in the drum changes, the valve 36 reduces or increasesthe flow of vapor in the tubes I6 and at the same time increases ordecreases the flow into the coil 4| placed in the water of the boilerdrum 62. The fan speed or damper regulator 5|, 52 will maintain thepressure of vapor by changing the how of gases through the heater 22.

, The return of condensate from the coil 4| and heating element 16 iseffected in substantially the same manner as described for the formshown in Fig. 1. To comply with the law, a safety valve 11 may be put onthe high pressure drum I0 and also on the circuit of the heatingsubstance (not shown) The natural circulation for such times as the highpressure steam is not needed, and both the fan 26 and the circulatingpump 21' are shut down, is effected by opening the valve 56in theby-pass pipe 55 which returns condensed vapor from the coil 4| and byloading the valve 36 with a deadweight to open the vapor circuit intothe coil 4! and to close the circuit into heat-.-. ing element. If thelatter were open, allthe heating substance from the-heater 22 wouldgradually be drained into the surge tank 28; The shortage of heatingsubstance in the circuit in the condition of natural circulation will bemanifested by too high a level in the surge tank 2! and a few secondsoperation of pump 21- will serve to restore the shortage. The drainingof the heating substance into the surge tank 28 during the long shutdowns of the boiler is'effected by the by-pass valve 18 in pipe". Thecheck valve 30 on the pump discharge prevents the emptying of the heater22 into the tank 28 when operating under-natural circulation.

The descaling. of the heating elements 16 may I claims.

down and damper 53 is closed while the auxiliary damper indicated 59 isopened. Next the valve 8| in line I0 is opened, valve 82 in line isshut, and valve ii in line 38 is opened. In these conditions the heatingsubstance circuit will be divided into two parts: the first partincluding heater 22, tank 28 and separator 32 will be under higher vaporpressure than the other part which contains both heating elements 16 and4!. To preclude any untoward rise of vapor pressure; in the isolatedflrstpart, cold air is admitted'into the furnace through the damper G9and the heater 22. The check valves 45 and 84, the closed valve 82 andthe opened valve 83 define. a natural circulation circuit comprisingboth the heating elements I! and 4|. Due to the high temperaturediiference between the drum Ill and the boiler drum where the coil 4| isimmersed, there will be a quick transfer of heat from the water in drum10 to the boiler water. Vapor in the tubes 18 will be boiling at atemperature very near to that at which it is condensing in the coil 4|.By opening the valve 83 last and uickly, a substantial quick cooling of'the tubes 16 from the inside will be effected which will be suflicientto break the scale sheath, which-may be afterward removed by opening theblowdown valves 1 I.

If there is a shortage of heating substance in the circuit, it may berestored by,cracking valve 56 such quantities of heat are withdrawn fromthe said heaters as are,necessary for the requirements in the saidheating zone and because any heat after being withdrawn and not utilizedis recovered in the heater furnishing the heat initially. v

Since changes may be made in the process and the several steps thereofand in the-forms of apparatus and the several parts thereof which aredisclosed herein, without'transcending the principles of the invention,it will be understood that no intention is entertained to limit theinvention except by the scope of the appended WhatIclaim is: g

1. Apparatus for supplying heat to a heater comprising a closed circuitfor the circulation of a high boiling point heating fluid, said circuithaving a portion thereof in said heater, a second heater in saidcircuit, a steam generator, means for withdrawing and conducting part.of the products of combustion from a high temperature portion of thefurnace of said generator to the second heater to heat the fluid flowingtherethrough prior to its flow through the first heater. means forreturning the withdrawn products of combustion to a low temperatureportion of said generator after passage through the second heater, meansfor controlling the quantity of products of combustionwithdrawn inresponse to the heating requirements of the first heater,

means for by-passing heated fluid around the first heater, means forcontrolling the by-pass in response to the heating requirements oi. thefirst heater, and means for recovering the heat from said by-passedfluid in the steam generator.

2. Apparatus tor supplying heat to a heater from a steam generator atirregular intervals in variable amounts at a temperature level abovethat of the saturated steam produced in the generator, comprising meansfor passing a high boiling point heating fluid through a second heater,means for withdrawing a portion of the products of combustion from ahigh temperature portion of the generator and passing said portionthrough the second heater to heat the heating fluid to vaporizationtemperature, means for controlling the quantity of products ofcombustion so withdrawn from the generator in response to the heatrequirements in the heater, means for separating the vaporized andunvaporized portions of the heating fluid, means for distributingthevaporized portion between the heater and a heat absorbing portion 01'the generator in such manner as to provide the required quantity oi!heat in the heater with excess heat being conducted to said heatabsorbing portion of the generator, and means for circulating theunvaporized portion of the heating fluid through the second heater toabsorb heat from the products oi combustion passing therethrough at suchtimes as heat is not required to be supplied to said heater.

3. Apparatus for supplying heat to a heater from a steam generator atirregular intervals in variable amounts at a temperature level abovethat oi. the saturated steam produced in the generator, comprising meansfor passing a high boiling point heating fluid through a second heater,means for withdrawing a portion of the products 01. combustion from ahigh temperature portion of the generator and passing said portionthrough the second heater to heat the heating fluid to vaporizationtemperature. means for controlling the quantity of products ofcombustion so withdrawn from the generator in response to the heatrequirements in the heater, means for returning the products ofcombustion so withdrawn to a low temperature point in the generator inthe path of flow oi the products of combustion, means for separating thevaporized and unvaporized portions of the heating fluid, means fordistributing the vaporized portion between the heater and a heatabsorbing portion of the generator in such manner as to provide therequired quantity heat in the heater with excess heat being conducted tosaid heat absorbing portion of the generator, and means for circulatingthe unvaporized portion of the heating fluid through the second heaterto absorb heat from the products oi combustion passing therethrough atsuch times as heat is not required to be supplied to said heater.

4. Method of descaling tubular elements disposed in contact bothinteriorly and exteriorly with heated fluids-under pressure and at leastpartially in the liquid phase, one of said fluids having scale formingconstituents, which comprises quickly lowering the pressure upon theother of said fluids to cause partial evaporation of said fluid, therebycooling said liquid and the tube surface in contact therewith, whilemain-- taining the pressure and temperature of the other fluidsubstantially constant, to thereby break the bond between the scale andtuba to remove the scale from the tubes.

NICHOLAS C. ARTBAY.

